Tuning-fork type electronic clock

ABSTRACT

An electronic clock making use of an electromagnetically actuated tuning fork whose vibrations are converted into rotary motion for driving the gear train of the clock by means of a motion transformer including a V-shaped indexing element. The ends of the indexing element are attached to the tines of the fork at corresponding points thereon, and the vertex thereof is flattened to define a rectangular tongue whose edge engages the ratchet teeth of an index wheel whereby as the tines vibrate, the tongue reciprocates in a rectilinear path at right angles to the direction of vibration. The index wheel is joined to a worm gear coupled to the first wheel in the gear train, the worm gear being supported for rotation between a fixed pivot and a spring-biased pivot, whereby sufficient friction is introduced to prevent retrograde motion of the index wheel.

United States Patent Van Haaften [451 Se t. 26, 1972 TUNING-FORK TYPEELECTRONIC Primary Examiner-Richard B. Wilkinson CLOCK AssistantExaminer-Edith Ct Simmons Jackmon [72] inventor: Egbert Van Haaften,Closter, NJ. Anomey Mlchael Ebert [73] Assignee: lylultr'aNiz'latchCompany, Inc., New 57 ABSTRACT or An electronic clock making use of anelectromagneti- [22] Flled: July 8,1971 cally actuated tuning fork whosevibrations are con- 211 AppL 160335 verted into rotary motion fordriving the gear train of the clock by means of a motion transformerincluding a V-shaped indexing element. The ends of the index- [52]"58/23 632 39 ing element are attached to the tines of the fork atcorresponding points thereon. and the vertex thereof 33 is flattened todefine a rectangular tongue whose edge 57 3 i engages the ratchet teethof an index wheel whereby as the tines vibrate, the tongue reciprocatesin a rectilinear path at right angles to the direction of [56]References Cited vibration. The index wheel is joined to a worm gearUNITED STATES PATENTS coupled to the first wheel in the gear train, theworm gear being supported for rotation between a fixed 3,425,210 2/1969Barth ..58/23R pivot and a springbiased pivot, whereby sufficl-em F R GPATENTS OR APPUCA'HQNS flrlictiocrli is inltrolduced to preventretrograde motion of t 1,519,243 2/1968 France ..58/23 TF em ex w ee 9Claims, 7 Drawing Figures IO 0 45, iii .0,

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I N VENTOR. time Hurray TUNING-FORK TYPE ELECTRONIC CLOCK BACKGROUND OFTHE INVENTION This invention relates generally to electronic timepiecesand more particularly to clocks incorporating anelectromagnetically-actuated tuning fork as a time base.

By definition, a watch is a portable timepiece designed to be worn orcarried on the person. Clocks on the other hand, are those devices otherthan watches for indicating or measuring time. Time measurement bymechanical means was first carried out by clocks employing pendulums asthe timekeeping standard, and only with the introduction of the balancewheel was it possible to produce compact timepieces or watches as wellas clocks. In modern spring-powered mechanical movements employingbalance wheels, both clocks and watches make use of essentially the sameoperating components, the main distinction therebetween lying in thescale of the components and the torque produced thereby, for clocksrequire a greater torque to drive the relatively large time-indicatinghands.

In the more recently developed field of electronic timepieces of thetype in which an electromagnetically actuated tuning fork functions asthe time base, the evolution of this timepiece has been the very reverseof that of mechanical timepieces, for the introduction of thetuning-fork watchpreceded the development of the tuning-fork clock.

In US. Pa't. No. 2,971,323 of Hetzel, there is disclosed an electronictimepiece suitable for a watch, and including a tuning fork having arelatively high frequency. A battery-powered transistorized drivecircuit acts to sustain the vibratory motion of the fork. Thereciprocating motion of the fork, which serves as a time-keepingstandard, is transformed into rotary motion by means of a ratchet andpawl mechanism whose index finger is attached to one tine of the fork.The finger engages and advances a ratchet wheel provided with a pinionfor operating the timepiece hands through a train of gears.

US. Pat. No. 3,184,981 of Bennett, Mutter, and Van Haaften discloses animproved form of a motion converter for a timepiece of the Hetzel type,whereby the ratchet wheel is caused to advance only one tooth for eachforward stroke of the index finger attached to the tine, regardless ofminor variations in the length of the stroke arising from changes in theamplitude of fork vibration. This is accomplished by means of anauxiliary pawl attached to the pillar plate of the timepiece, the pawlengaging the ratchet wheel at a position relative to the index finger atwhich the phase between the finger and pawl is several ratchet teethplus one-half tooth. Motion converters of this type operate efficientlyand reliably, and are presently used in tuning fork watches soldcommercially under the trademark, Accutron.

Electric clocks whose timing is synchronized by the frequency of the ACpower source, may be manufactured and sold at low cost, for such clocksdo not require motors of high quality to maintain accurate timing. Butwhen a battery-operated clock is required in those situations where ACpower is not available or where the use of external power line isundesirable, existing low-cost battery-operated clocks usually fail toafford accurate timing comparable to that of an electric clock,particularly when use is made of a balance wheel.

But when the tuning fork principle is applied to electronic timepiecesin clock form, the relatively delicate index finger auxiliary pawlratchet wheel arrangement, which requires careful adjustment, may not besuitable for a low-cost clock, particularly for clocks intended for asomewhat rugged environment such as the dashboard of a vehicle. It mustbe borne in mind that while clocks are larger than watches, clocks aregenerally marketed at a much lower cost in that watches, because oftheir fine workmanship, are treated as jewelry items, whereas clocks arehousehold or industrial articles. Hence expensive mechanisms which areacceptable for fine watches cannot, as a practical matter, be used in alow-cost clock.

In an attempt to overcome these drawbacks, batteryoperated tuning-forkclocks have been developed, making use of so-called magnetic escapementsto convert the vibratory motion of the fork into rotary motion, ratherthan mechanical motion converters of the type disclosed in theabove-identified patents. However, a magnetic escapement wherein a wheelhaving a magnetic track or teeth is associated with magnets secured tothe vibrating tines of the fork, has serious disadvantages, for suchescapements are inefficient and produce relatively little torque.Moreover, they are not self-starting and it is necessary to include amechanical starter in the clock to set the wheel of the magneticescapement into motion.

Also characteristic of existing tuning-fork watches is a tuning forkoperating in conjunction with two electromagnetic transducers, one beingformed by a magnetic cup attached to one tine of the fork, andassociated with a stationary coil, and the other being a second magneticcup attached to the other tine and as sociated with another stationarycoil. This tuning fork and transducer assembly is relatively costly anda scaled-up version for a clock would result in high manufacturingcosts.

SUMMARY OF THE INVENTION In view of the foregoing, it is the main objectof the invention to provide a tuning-fork type electronic clock which isaccurate and reliable in operation, and which may be produced and soldat low cost.

More specifically it is an object of this invention to provide anefficient and rugged motion transformer for an electronic clock of theabove-described type, which converter is capable of operatingsuccessfully under arduous environmental conditions.

Also an object of this invention is to provide a simple, low-costelectromagnetic transducer for a tuningfork electronic clock, whichtransducer is composed of coil and magnet assemblies that may be readilyattached to the tines of the fork.

Yet another object of the invention is to provide a tuning fork which isfabricated from a single piece of strip metal and which may be quicklyinstalled or dismounted.

Briefly stated, these objects are attained in an electronic clockcomprising a tuning fork having a permanent magnet assembly secured toone tine thereof, and a coreless coil assembly secured to the other tinethereof, the magnet being inserted in the coil to provide anelectromagnetic transducer for sustaining the fork in vibration. Bridgedbetween the tines is a V-shaped indexing element whose ends are securedto corresponding points on the tines and whose vertex is flattened todefine a rectangular tongue, the lower edge of which engages the ratchetteeth of an index wheel. The tongue is caused to undergo rectilinearmotion at right angles to the direction of tine vibration, thereby todrive the index wheel. The index wheel is mounted on a worm gearsupported between end pivots, one of which is spring-biased to createsufficient friction preventing retrograde movement of the index wheel.The worm gear engages the first wheel in a gear train serving to drivethe hands of the clock.

OUTLINE OF THE DRAWING For a better understanding of the invention aswell as other objects and further features thereof, reference is made tothe following detailed description to be read in conjunction with theaccompanying drawing, wherein:

FIG. I is an elevational rear view of a tuning-fork type electronicclock in accordance with the invention;

FIG. 2 is a schematic diagram of the electrical circuit associated withthe tuning fork in the clock;

FIG. 3 is a section taken through the clock structure;

FIG. 4 is a separate perspective view of the tuning fork and itsassociated electromagnetic transducer;

FIG. 5 is a perspective view of the indexing element associated with thefork;

FIG. 6 is a plan view of the indexing element and the ratchet wheeldriven thereby; and

FIG. 7 is a sectional view of the electromagnetic transducer associatedwith the tines of the tuning fork.

DESCRIPTION OF THE INVENTION Referring now to FIG. 1, there is shown atuning-fork type electronic clock in accordance with the invention,comprising a U-shaped fork generally designated by numeral 10, having apair of tines 10A and 108. The fork is constructed of a single strip ofmetal having indentations at nodal points 10C and 10D adjacent the base108. The fork is attached to a mounting post 11 by a pair of tabs 12,each of which is bent to embrace base 10E. Mounting post 11 is anchoredin pillar plate 13.

The free ends of tines 10A and 10B are provided with cut-outs to definemounting fingers for holding a coil assembly 14 and a magnet assembly15, which together constitute the electromagnetic transducer forsustaining the fork in vibration. The operating frequency of the fork ispreferably 180 Hz, for while the clock is designed for batteryoperation, at this frequency it becomes possible to synchronize theoperation of the fork from a 60 Hz power line (60 Hz is an integralsubmultiple of I80 Hz), thereby providing a timepiece of high accuracy.But should AC power fail, the fork would still continue to functionaccurately on battery power. In practice, sync pulses may be derivedinductively from the power line, thereby avoiding the need for a wiredconnection thereto.

The vibratory action of the fork is converted into rotary motion by amechanical motion transformer constituted by a generally V-shapedindexing element 16, whose ends are attached at corresponding positionsto tines 10A and 10B, the ends fitting into holes in the tines and beingepoxied or otherwise bonded thereto. The indexing element in practice ispreferably made from a single piece of stainless steel round wire havinga diameter of 0.006 inches.

The round wire is flattened at the vertex of the indexing element todefine a vertically oriented rectangular tongue 16A, and the ends of theelement are bent outwardly and flattened to define vertically orientedfeet 168 and 16C. The sides of the indexing element are also flattenedto define horizontally oriented legs 16D and 16E, whereby all thatremains round in the wire are the links between the legs and the feet,and the links between the legs and the tongue.

As the vibrating tines move toward and away from each other, flexureoccurs in the feet 168 and 16C of the indexing element, causing tongue16A joined to legs 16D and to undergo rectilinear motion at right anglesto the motion of the tines. Since both tines oscillate to an equalextent, tongue 16A will move a distance equal to the distance travelledby an individual tine at the point at which the feet (163 and 16C) areconnected thereto. Thus, as best seen in FIG. 6, the tines vibrate, thetongue of the indexing element in the course of each cycle executes aforward stroke along the longitudinal axis of the fork and a returnstroke along the same axis.

The lower edge of tongue 16A of the indexing element engages the ratchetteeth on an index wheel 17 such that with each forward stroke of thetongue the wheel is advanced one increment. The tuning fork has nopivots or bearings and its timekeeping action is therefore independentof the effects of friction. The amplitude of the fork tines is chosen sothat the movement of tongue 16A is about one and one half times thedistance between successive teeth on the index wheel. However, no pawlis used to prevent retrograde motion of the wheel. Such retrogrademotion is prevented by a frictional bearing for the index wheel.

Index wheel 17 is integral with a worm gear 18, the two elements beingpreferably made of high-strength, low-friction plastic material, such asDelrin. The worm gear is mounted for rotation between two tapered pivots19 and 20, which project into holes bored in the opposite ends of theworm gear. Pivot 19 is rigidly supported whereas pivot 20 is borne onthe free end of a flat spring 21, mounted on a bracket 22. Spring 21 ispre-stressed to apply axial pressure against the worm gear. In practice,the pivots are formed of hardened, highly polished stainless steel andare pointed to a 20 included angle.

The direction of pitch in the worm is chosen so that as it rotates,should there be any load imposed on the index wheel and the wormintegral therewith, its direction is toward the fixed pivot 19, therebypreventing the worm from moving away from the fixed pivot under loadconditions. The resultant combination of forces (that of friction at thepivots and the lesser friction of the indexing element and index wheel),prevents retrogression of the wheel during the return stroke of theindexing head.

Because the teeth in the ratchet wheel are engaged by the broad loweredge of the tongue, shock or vibration causing lateral displacement ofthe tongue relative to the wheel will not effect disengagementtherebetween. The indexing element is downwardly biased against theindex wheel which also serves to present disengagement therebetween.Thus the clock is capable of uninterrupted operation under the mostarduous field conditions, for the clock includes no delicate balancewheel or motion transformer that may be rendered inoperative or upset byshock forces.

lntermeshing with worm gear 18 is a worm wheel 23 mounted on a centershaft 24 whose end, as shown in FIG. 3, terminates in the second hand 25of the clock. The various time-indicating hands are associated with adial plate 26. Worm wheel 23 has sixty teeth, the worm gear having asingle lead pitch. Index wheel 17 has one hundred and eighty teeth tomatch the 180 Hz fork frequency. With this combination, worm wheel 23makes one revolution per minute so that the second hand completes a fullturn every minute.

Also keyed to shaft 24 directly at a position below worm wheel 23 is apinion 27 having six teeth which, in turn, drives a sixty-tooth gear 28.Gear 28 rotates on a shaft 29 and is fitted to a IO-tooth pinion 30through a slip clutch arrangement that permits the setting of the handswithout disturbing the driving portion of the train.

The l0-tooth pinion 30 drives a 60-tooth gear 31 provided with al6-tooth pinion 32. Fastened to the gear assembly is a tubular shaft 33concentric with center shaft 24 and carrying the minute hand 34. The16-tooth pinion 32 drives a 48-tooth gear 35 having a pinion 36 providedwith 14 teeth, pinion 3.6, in turn driving a 56-tooth gear 37 carryingthe hour hand 38.

Gear 35, commonly called the minute wheel, which is combined with pinion36, operates on the same shaft 29 as the clutch gear 39. This simplifiedarrangement is advantageous, for only one critical center distance forthe gears is required, outside that of the worm and index wheelassembly. An idler gear is required in the hand-setting arrangement, butthis is not critical as far as center distance is concerned.

In the above described gear train assembly, all parts thereof may befabricated of good-grade plastic material except for the two mainarbors, which are preferably of stainless steel. By using Delrin for allplastic parts and stainless steel for all metal-bearing parts, one isable to dispense with the need for a lubricant.

Coil assembly 14, as shown separately in FIG. 7 is constituted by atubular coil form divided by an annular partition 41 into two sections,one having a drive coil 42 wound therein, and the other a phase-sensingor pick-up coil 43. In practice, since the drive coil has more turnsthan the phase-sensing coil, a portion of the phase-sensing form sectionmay be occupied by drive coil turns, so that the drive coil is then madeup of two series-connected parts.

Coil form 40 is provided with a cylindrical extension 44 projectingaxially from one end thereof, which extension has one groove 44A adaptedto receive the U- shaped cut-out on the end of tine A, and a secondgroove 448 for accommodating a timing regulator 45.

This regulator is in the form of an unbalanced loading mass constitutedby a round piece of wire with a loop and a circular portion to fit intothe coil form groove, such that by turning the regulator to differentangular positions, the orientation of the unbalanced loading mass isshifted to bring about a fine adjustment in timing.

The three wires from coils 42 and 43 are connected to an electroniccircuit housed in a module 46 secured to the pillar plate. The wiresfrom coil assembly 14 run along the length of tine 10A and are fastenedthereto,

the wires at the nodal point 10C then leaving the tine to go to module46. Since there is virtually no motion at nodal point 10C, negligibleflexing of the wires is experienced despite the fact that the tinecarrying the wires is in constant vibration.

Magnet assembly 15 is constituted by three parts, namely a permanentmagnet rod 47, a mounting plug 48, preferably made of brass and cementedor otherwise bonded to one end of the magnet rod, and a regulator 49.Because the plug is made of non-ferromagnetic material, the openmagnetic flux path extends from the magnet rod, coaxially disposedwithin coils 42 and 43 through these coils, but is magnetically isolatedfrom tine 108 on which the magnet assembly is mounted.

Plug 48 is provided with a groove to receive the cutout in tine 10B anda groove 488 to receive the regulator 49, which is identical in form andfunction to regulator 45 on the coil assembly.

The electronic circuit housed in module 46 is powered by a replaceablebattery cell 50, held in a suitable socket or by clips on pillar plate13. The circuit, as shown in FIG. 2, is constituted by a transistor 51,whose emitter is connected to the positive pole of battery 50, thenegative pole thereof being connected through drive coil 42 to thecollector of the transistor. The negative pole is also coupled throughphasesensing coil 43 and through a resistance-capacitance bias circuit52 to the base of the transistor. A bypass capacitor 53 is connectedbetween the emitter and the junction of the phase-sensing coil 43 andthe RC bias circuit 52 to prevent parasitic oscillation.

In operation, when transistor 51 is rendered momentarily conductive, acurrent pulse derived from battery 50 flows through drive coil 43. Theresultant magnetic field produces an axial thrust on magnet assembly 15,this action producing an equal and opposite reaction on the coilassembly 14. Since magnet assembly 15 is mounted on tine 10B and coilassembly 14 on tine 10A, the tines are deflected in opposing directions.

The movement of the magnet and coil assemblies relative to each otherinduces a back EMF both in drive coil 42 and in phase-sensing coil 13.Since this reciprocation is in accordance with fork motion, the back EMFassumes the form of an alternating voltage whose frequency correspondsto fork frequency (i.e., Hz). The voltage induced in sensing coil 43 isapplied to the base of the transistor and overcomes a bias imposedthereon by the RC circuit, thereby to control the instant or phaseposition in the course of each cycle when the drive pulse is to bedelivered to the drive coil.

The back EMF developed in the drive coil is in series opposition to thevoltage applied by battery 50 between emitter and collector of thetransistor. Battery voltage has a constant value, whereas the back EMFis a function of tine amplitude. The operation of the transistor duringits conductive periods is controlled in accordance with the algebraicsum of the battery and back EMF voltage applied thereto, and theamplitude of the fork vibration is thereby regulated. The behavior ofthis and similar circuits is explained more fully in Hetzel US. Pat. No.2,971,323, commonly assigned.

The operating frequency of the fork is determined not by the fork perse, but by the combined mass of the tines and the assemblies mountedthereon. For highest operating efficiency, it is essential that symmetryexist as between the centers of gravity of the two oscillating masseswith respect to the axis of symmetry of the fork. in practice,therefore, magnetic assembly is made such that its mass and center ofgravity substantially match that of the coil assembly 14.

While there has been shown and described a preferred embodiment of atuning fork clock in accordance with the invention, it will beappreciated that many changes and modifications may be made thereinwithout, however departing from the essential spirit of the invention.For example, the indexing element, rather than being made of round wireas described herein, with flattened sections, may be made entirely offlat wire twisted at appropriate points to define the flat lip andtongue sections of the element.

l claim:

1. An electronic timepiece comprising:

A. a tuning fork having a pair of tines,

B. means operatively coupled to said fork to sustain said fork invibration at its natural frequency, and

C. means including a motion transformer to convert the vibratory actionof said fork into rotary motion for driving a gear train coupled totime-indicating hands, said means including a V-shaped indexing elementwhose ends are secured to the tines at corresponding points thereon,whereby the vertex of the element is caused to reciprocate in arectilinear path substantially at right angles to the direction of tinemotion, a ratchet wheel mounted on a worm gear, the teeth of said wheelbeing en gaged by the vertex of said element whereby with each forwardstroke thereof, said wheel is advanced one increment, said worm gearengaging the first wheel in said gear train and being mounted forrotation on a friction bearing introducing sufficient drag to preventretrograde motion of the ratchet wheel on the return stroke of thevertex.

2. A timepiece as set forth in claim 1, wherein said vertex isconstituted by a rectangular tongue whose lower edge engages said teeth,said tongue lying in a plane transversely disposed relative to saidrectilinear path.

3. A timepiece as set forth in claim 2, wherein said V- shaped indexingelement is formed by a piece of round wire whose ends are bent outwardlyand are attached to said tines, the vertex being flattened to definesaid tongue.

4. A timepiece as set forth in claim sides of said element are alsoflattened.

S. A timepiece as set forth in claim 1, wherein said frictional bearingis formed by two tapered pivots received in bores in the ends of saidworm gear, one pivot being fixedly mounted, the other being springbiasedto urge said worm gear in the direction of the fixed pivot.

6. A timepiece as set forth in claim 5, wherein the direction of thepitch of said worm gear is such that any load imposed on the gear isdirected toward the fixed pivot, thereby preventing the worm from movingaway from the fixed pivot under load conditions.

7. A timepiece as set forth in claim 1, wherein said means to sustainsaid fork in vibration includes an electroma etjc transducer coupled toan electronic drive circui said transducer being constituted by a magnetassembly mounted on one tine of said fork and cooperating with a coilassembly mounted on the other tine.

8. A timepiece as set forth in claim 7, wherein said magnet assembly isconstituted by a permanent magnet rod secured to the associated tine bya non-ferromagnetic spacer, whereby said magnet rod is magneticallyisolated therefrom.

9. A timepiece as set forth in claim 8, wherein said spacer includes acircular groove and a timing regulator in the form of an unbalanced masssupported in said groove and including a wire loop encircling saidgroove.

3, wherein the

1. An electronic timepiece comprising: A. a tuning fork having a pair oftines, B. means operatively coupled to said fork to sustain said fork invibration at its natural frequency, and C. means including a motiontransformer to convert the vibratory action of said fork into rotarymotion for driving a gear train coupled to time-indicating hands, saidmeans including a Vshaped indexing element whose ends are secured to thetines at corresponding points thereon, whereby the vertex of the elementis caused to reciprocate in a rectilinear path substantially at rightangles to the direction of tine motion, a ratchet wheel mounted on aworm gear, the teeth of said wheel being engaged by the vertex of saidelement whereby with each forward stroke thereof, said wheel is advancedone increment, said worm gear engaging the first wheel in said geartrain and being mounted for rotation on a friction bearing introducingsufficient drag to prevent retrograde motion of the ratchet wheel on thereturn stroke of the vertex.
 2. A timepiece as set forth in claim 1,wherein said vertex is constituted by a rectangular tongue whose loweredge engages said teeth, said tongue lying in a plane transverselydisposed relative to said rectilinear path.
 3. A timepiece as set forthin claim 2, wherein said V-shaped indexing element is formed by a pieceof round wire whose ends are bent outwardly and are attached to saidtines, the vertex being flattened to define said tongue.
 4. A timepiEceas set forth in claim 3, wherein the sides of said element are alsoflattened.
 5. A timepiece as set forth in claim 1, wherein saidfrictional bearing is formed by two tapered pivots received in bores inthe ends of said worm gear, one pivot being fixedly mounted, the otherbeing spring-biased to urge said worm gear in the direction of the fixedpivot.
 6. A timepiece as set forth in claim 5, wherein the direction ofthe pitch of said worm gear is such that any load imposed on the gear isdirected toward the fixed pivot, thereby preventing the worm from movingaway from the fixed pivot under load conditions.
 7. A timepiece as setforth in claim 1, wherein said means to sustain said fork in vibrationincludes an electromagnetic transducer coupled to an electronic drivecircuit, said transducer being constituted by a magnet assembly mountedon one tine of said fork and cooperating with a coil assembly mounted onthe other tine.
 8. A timepiece as set forth in claim 7, wherein saidmagnet assembly is constituted by a permanent magnet rod secured to theassociated tine by a non-ferromagnetic spacer, whereby said magnet rodis magnetically isolated therefrom.
 9. A timepiece as set forth in claim8, wherein said spacer includes a circular groove and a timing regulatorin the form of an unbalanced mass supported in said groove and includinga wire loop encircling said groove.